Capillary viscometer



Feb. 29, 1944. E. P. lRANY CAPILLARY VISCOMETER Filed Nov. 20, 1943 /N-vE/v Tof? .ER/vaar PAUL /femw TTORN'E-Y low viscosities.

Patented Feb. 29, 1944 UNITED `STATE s PATENT olflflcl?.`

cAPmLARY vlsooMETER Ernest Paul Irany, Shawinigan Falls,

Quebec, Canada Application November 20, 1943, Serial No. 511,187

In Canada October 29, 1943 Claims.

INTRODUCTION This invention relates to a capillary viscometer. Capillary viscometers which are available in yseveral standardized (fypes are accurate if used Capillary viscometers -of` the usual design-forv example, the Ostwald type pipette-fail to give correct readings of viscosities below about-1 centipoise. Due to the above-mentioned iniiuences which tend to-delay the passage of the liquid through the instrument, the computed Viscosities are always too high and errors increase with the fluidity of the liquid.

Moreover, the usual type of capillary viscometer employing the out-flow principle embodies a tube of considerable length. This means that the instrument is far from compact and where it must` beimmersed in a bath to achieve a working temperature the entire equipmentinvolved in the viscosity measurement becomes cumbersome.

OBJECTS A principal object of the invention is thev achievement of accuracy inv the measurement of A further object of the invention is to provide a viscometer which is unusualtrating two forms of such preferred apparatus, in which:

Figure 1 illustrates an instrument corresponding in capacity to-the normal Ostwald type viscometer. n V I V- Figure 2 illustrates aninstrument adapted for very close measurements of low viscosity liquids. Referring more particularly to Figure lof the drawing, the instrument illustrated-includes a straight glass tube I'I having a bulb l2 at the bottom thereof serving as a recipient vessel. Ex-

tending from the bulb I2 downwards and then upwards in the yform of a helix or spiral is a tube I4 having a calibrated capillary IMI preferably of not less th'an .35 millimeter inside bore. The

top end of this'tube isprovided with a feeder bulb I5 and extending upwards from the top of the bulb a tube Il. Just above the bulb I5 on the tube Il is a measuring mark mvand just below the bulb I5 on the tube I1 is a measuring mark y. The capillary tubev I4 is adapted to present a circumfluent path to liquid flowing from the bulb I5 towards the bulb I2. Preferably as indicated in the drawing, at least a portion of vthis path has an inclinationof less than towards the horizontal when the viscometer is in operative position.

ly compact for a given range. It is a still further object of the present invention to provide an inexpensive capillary viscometer which can be operated as easily as the conventional type of vislcosity pipette but which can be used for the precise measurement of the lowest viscosities encountered in liquids. It is a further object to promote practical applications of viscometry in many fields of process and product control which heretofore were excluded because of the lack of asuitable instrument.

THE INVENTliON vThese and other objects of the invention are l accomplished by a viscometer having a capillary of which the total length is substantially greater than the vertical distance between its terminals. This'is accomplished according to a preferred structure in which the capillary has a spiral form.

The invention Will be further understood by reference to the accompanying drawing, illus- Operation A measured amount of liquid is introduced into the tube I Iv and slight air or gas pressure applied thereto until the liquid rises in the capillary Ha through; th,` bulb I5 and above the mark :c on `the tube Il: The pressure is then removed and the liquid allowed to,y flow past the marks :c and y. Thetime lof passage from the mark at to the mark y is/'r'egistered The viscosity is then found by comparing the outow time with that of a liquid of known viscosity. It is to bey observed that the volumes of the upper bulb Il of the capillary and of the/ lower bulb I2 must be so related that, by using a convenient amount/'of liquid, .the lower meniscus remain within, and near the center of, the lower bulb I2. `It is also seen that the circuitous form of the ycapillary tube presents a circumuentpath to ,the liquid. l

A viscometer asdescribed, having a capillary f of about the .same inside diameter as that used in the standard type Ostwald pipette, and having about the same outflow time,'wou1d require only one-half of the height of the latter with only a.

Vnegligible increase in lateral dimension. compact construction would eiect even far great- This er economyl in the size of the thermostatic bath, reducing the necessary volume of the latter to about one-fifth or less.

ALTERNATE FORM Operation `A measured amount of liquid is introduced into the feeder tube 2| and the bulb 22 through the calibrated pipette 41 and the three-way cock 40. The cock 40 is then set to communicate between the bulb 35 and the pipette 41. Slight air or gas pressure is applied through the tube 50 by opening the cock 52 until the liquid rises through the capillary above the bulb 35 to a point-above the mark a. The lower surface of the liquid will lie Within the bulb 22. The cock 52 is then closed and the cock 40 turned so as to join the space above the two levels of the liquid and to seal it from the outside. The time `of passage of the meniscus from a to b is registered. The viscosity is then determined by comparing the outflow time with that of a liquid of known viscosity. In viscosity measurements of this type, a viscometer according to the present invention has been found to be twelve times more sensitive than an Ostwald pipette.

EXAMPLE The following example in which a characteristic procedure is carried out on a preferred type of viscometer according to the invention in comparison with a similar procedure on a standard viscometer of the same capacity further illustrates the invention. 'Ihis example should not be taken as limiting the scope of the disclosure but only as illustrative.

The following comparison was made between a viscometer of the type illustrated in Figure 1 and a commercial Ostwald pipette. The figures of the drawing are used for convenience to identify the parts of the former. The applicants viscometer had a capillary of .45 millimeter inside diameter and 600 millimeters in length, shaped into a helix of 120 millimeters in height. The Ostwald pipette had a straight vertical capillary of .50 millimeter bore and 90 millimeters length. The applicants viscometer gave accurate readings of a viscosity of 0.223 centipoise (acetaldehyde at 20 C.). The Ostwald pipette showed a positive error of more than 7% with the same test liquid.

' ADvANrAGEs One skilled in the art will realize the advantages of the devices according to the applicants invention. They permit the convenient handling of liquids of 'low boiling point which may be kept under pressure if desired. Their compactness for a given capacity and sensitivity allows accurate determinations of low viscosity liquids downto the iinest limits. Their relatively compact nature also makes them Vparticularly suitable for use alone in the customary water bath or in combination with a thermostatic device. Many other advantages will be evident.

It will-be understood that, without departing from the spirit of the invention or the scope of the claims, various modifications may be made in the specific expedients described. The latter areillustrative only and not offered in a restricting sense, it being desired that only such limitations shall beplaced thereon as may be required by the state of the prior art.

I claim:

l. A viscometer of the outflow type, comprising, an upright capillary tube, a' recipient vessel having a connection with the lower end of said capillary tube, a calibrated bulb having a connection with the upper end of said capillary tube, a passage adapting said recipient vessel to be connected with a pressure source, portions of said capillary tube above the recipient vessel being circuitous thereby to present a circumfiuent path to liquid passing from the calibrated bulb to the recipient vessel.

2. A viscometer as claimed in claim 1, wherein Y the capillary is of spiral form. i

' passage of a certain volume of liquid and a recipient vessel adapted to receive the liquid, a capillary tube extending between said bulb and said vessel, the capillary tube having a length considerably greater than the vertical distance between the bulb and the recipient vessel, a calibrated pipette,v a connection between said-pipette and said recipient vessel, a connection between said pipette and said calibrated bulb, a three-way cock controlling said connections whereby the pipette may be connected to or disconnected from either the recipient vessel or the calibrated bulb, a pressure inlet to said recipient vessel, and a cock for controlling said pressure inlet whereby pressure may be introduced to said recipient vessel or the latter may be cut ofi from the atmosphere.

4. A viscometer of the outflow type, comprising, a bulb calibrated for the observation oi the passage of a certain volume of liquid and a recipient vessel adapted to receive the liquid, a

capillary tube extending between said bulb and said vessel, the capillary tube having a length considerably greater than the vertical distance between the bulb and the recipient vessel, calibrated pipette, a connection between said ipette and said calibrated bulb, means `for conrolling said connections whereby the pipette ay be connected to or disconnected from either the recipient vessel or the calibrated bulb, a pressure inlet to said recipient vessel, andl means for controlling said pressure inlet whereby pressure may be introduced to said recipient vessel or the latter may be cut olf from the atmosphere.

5. A viscometer of the outflow type, comprising, an upright capillary tube, a recipient vessel having a connection with the lower end of said capillary tube, a calibrated bulb having a connection with the upper end of said capillary tube, a passage adapting said recipient vessel to be connected with a pressure source, portions of said capillary tube above the recipient vessel being circuitous thereby to present a circumiluent path to liquid passing from the calibrated bulb to the recipient vessel, at least a portion of said capillary being so disposed that it has an inclination of less than 45 towards the horizontal when the viscometer is in operative position.

ERNEST PAUL IRANY. 

